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The app-based approach to adhesion

The speaker: Prof Steven Abbott runs his own company TCNF whilst being a Visiting Prof at U Leeds. He is trying to give away as much of his knowledge as possible via apps and eBooks, though his RSC “popular science” book Sticking Together: The Science of Adhesion isn’t free”.

There are many misapprehensions about how to achieve the adhesion you require. And even if you find the correct theory, it can be hard to understand it. Via a set of on-line apps, much of the mystery of obtaining good adhesion disappears, allowing formulators to focus on the things that matter. The talk will use some of the speaker’s large set of free apps live, showing how attendees can use them for their own formulation challenges. Links to the apps and to a handy set of YouTube demonstrations will be provided.

Tailoring the tack adhesion of Pressure-Sensitive Adhesives through stratification by formulation and processing

Toby R. Palmer 1, Hanne M. van der Kooij 2, Mathis Duewel 3, Katja Greiner, Joris Sprakel 2, Joseph L. Keddie1

1 Department of Physics, University of Surrey, Guildford, Surrey, GU2 7XH, UK

2 Department of Physical Chemistry and Soft Matter, Wageningen University, Wageningen, The Netherlands

3 Synthomer Germany GmbH, Marl, Germany

The use of pressure-sensitive adhesive (PSA) films is wide ranging, with applications including labels, tapes, and graphics. To achieve good adhesion, there needs to be a balance of viscous and elastic properties. There is some evidence in the literature that a gradient in composition of PSAs can lead to superior properties. One way to achieve a gradient in composition is through a multi-layered structure, requiring multiple depositions one on top of the other. This process can be time consuming and expensive for manufacturers.

We have investigated the application of diffusiophoresis-driven stratification in waterborne colloidal dispersions containing two types of particles having differing sizes, to tailor the properties at the top and bottom of a film. Diffusiophoresis is the motion of one species in a concentration gradient of another. Larger, dissipative particles from a commercial adhesive were blended with smaller, elastic poly(butyl acrylate) particles. We investigated both the formulation of the adhesives (i.e. the mass ratio of large to small particles and the size of the small particles) and the processing conditions (i.e. evaporation rates) in order to map out a range of parameters for which stratification is observed.

We used atomic force microscopy to qualitatively study the top surface of dry PSA films and to quantify the extent of any stratification. We performed probe tack testing to characterise the adhesive properties as a function of the stratification that has been observed. Our results were interpreted with reference to a diffusiophoresis model put forward by Sear and Warren (Phys. Rev. E 96, 062602 (2017)), that predicted the volume fraction of small particles and film formation conditions required for stratification of the small particles onto the top surface. By increasing the evaporation rate for the same composition, we found that the adhesive properties transition from solid-like to viscoelastic and tacky. For a given evaporation rate, we found that increasing the concentration of the elastic particles had the opposite effect, transitioning the film behaviour from that of an adhesive to that of a coating. Our results suggest that the properties of PSAs can be finely controlled through both processing and formulation changes to create stratified structures. Our results will aid the future design of multi-layered, single-deposition films.

Probing the Interface Between Organic Crystals

Alex Moldovan, Cambridge Crystallographic Data Centre

The adhesive and cohesive properties of organic particles play a crucial role in the manufacturing and performance of drug products. These can cause a powder to agglomerate during processing or an inhalation drug to inadequately deliver the required dose of the active pharmaceutical ingredient.

Surfaces of the particle influence the balance between the two forces, driven by surface chemistry and topology. Here we demonstrate a tool that allows us to predict surface-surface interactions using computational methods, which then estimate the interparticle cohesive-adhesive balance (CAB). To validate the model, we have carried a case study using atomic force microscopy where the adhesion between organic surfaces was measured.

Role of mucoadhesive polymers in retention of toothpaste in the oral cavity

Sam Aspinall1, Jane Parker2 and Vitaliy Khutoryanskiy1

1University of Reading, School of Pharmacy, UK

2University of Reading, School of Food, UK

Toothpastes are one of the most sophisticated pharmaceutical formulations available with a range of active and inactive ingredients balanced to create a product that is capable of fulfilling a multitude of roles. Although toothpastes are effective at what they do, improvements to the retention time of the active ingredients and flavour compounds would yield an improved therapeutic effect and leave the user with fresher breath, a refreshing feel and more confidence for a longer portion of their day.

The aim of this project is to look at the use of mucoadhesive polymers added to these formulations to create a novel toothpaste that has better retentive properties in the oral cavity than current commercial toothpaste. Retaining toothpaste for longer will increase the retention time of active ingredients on the mucosal and enamel surfaces of the oral cavity, allowing the active ingredients to stay at their active sites for longer periods. This in turn will have the ability to promote oral health and potentially lowering dental costs for millions worldwide. In addition to this, methodologies capable of measuring the retention of formulations in vitro will improve our understanding of where in the oral cavity does toothpaste retains and how it interacts with the different mucosal surfaces present.

Formulations capable of longer retention times in the oral cavity than current commercially available dentifrice were developed in addition to in vitro methodologies for measuring the retention of toothpastes, oral care products and gels. By formulating a range of novel toothpaste made with different mucoadhesive polymers, their retention on mucosal surfaces and physical properties can be measured. Formulations made from Carbopol ETD 2020 and Carbopol Ultrez 10 had significantly longer retention times than commercial formulations and other novel formulations tested.

Re-usable thermally reversible crosslinked adhesives

Prof Andrew Slark, Chemistry Department, University of Sheffield, Sheffield, UK

Crosslinked polymers provide the best mechanical properties and durability but have a negative environmental impact, since their permanent structure prevents easy separation and recycling of bonded components at their end-of-life. The EPSRC Manufacturing Fellowship - Innovative Coatings and Adhesives for Recycling (I-CARE) - is researching new smart polymers which not only target high performance in use but also can be triggered at their end-of-life to enable the re-use and recycling of valuable materials.

Our first proof of concept shows the design and performance of thermally reversible crosslinked adhesives from polyester and poly(ester urethane) Diels-Alder networks. Functional prepolymers and crosslinkers were synthesised with high atom efficiency via facile, industrially scalable techniques. The materials crosslink at ambient temperature and are thermally reversible above 100 °C. Adhesives were applied from the melt and cured under ambient conditions. The mechanical properties of the networks were tuneable by changing the prepolymer compositions. The crosslinked adhesives provided versatile adhesion on wood, plastic and aluminium, and were creep resistant up to 80 °C. The adhesives were thermally stable during application and could be re-used repeatedly in a facile manner by multiple bonding-debonding-rebonding cycles. The bond strengths achieved after repeated re-use were the same as the initial level of performance for networks with higher crosslink density.

This opens the possibility for the considered design of smart, sustainable crosslinked adhesives for a variety of applications. I-CARE aims to create a key body of knowledge by

  • investigating a range of scalable chemistry with different dynamics
  • creating key materials structure-property relationships
  • triggering the reversibility in a controlled but scalable manner

Bio-based adhesives: Binders from renewable resources

Dr. Lydia Heinrich, Wallenberg Wood Science Centre / Coating Technology; KTH Royal Institute of Technology, Stockholm

Introducing bio-based content into adhesive formulations is becoming increasingly important with a view to a circular economy and the reduction of carbon footprints. The most promising route to achieve this transition is through utilising the unique properties of renewable materials to optimize adhesive performance. Thus, a thorough understanding of the behaviour of bio-based compounds and their influence on adhesion needs to be developed. Herein, we present the use of lignin and hemicellulose-containing wood hydrolysate, both waste products from the pulp and paper industry, as binders for adhesives. Their rheological behaviour, polarity and thermal behaviour was characterised, and their potential for joining wood surfaces was assessed. Finally, chemical modifications and crosslinkers were used to improve adhesive strength.

Innovative adhesive solutions made from renewable sources

Renke Bargmann, BU Electronics, tesa tape (Suzhou) Co., Ltd

As a multinational company, tesa has been developing innovative adhesive tapes and self-adhesive system solutions for various industries, commercial customers, and end consumers. Today, the focus is on sustainability and energy-saving processes. tesa invests in the development of environmentally friendly products and solvent-free manufacture processes as well as in the use of renewable energy sources at its locations.

Creating adhesives from renewable sources is rather simple if your goal is to market yourself with biobased solutions. The challenges start with looking in the supply chain and evaluating the impacts of these materials on the environment and the society. This presentation will give a brief look into topics which should be considered in developing adhesives from renewable resources.